> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fincept.in/llms.txt
> Use this file to discover all available pages before exploring further.

# Calculate Tail Dependence Coefficient

> Measures the probability that two assets experience extreme losses simultaneously. Tail dependence is critical for portfolio diversification as assets may appear uncorrelated in normal times but become highly correlated during market crashes. Essential for risk parity strategies and crisis risk management. [Tier: PRO, Credits: 5]



## OpenAPI

````yaml api-specs/risk.json post /quantlib/risk/tail-risk/tail-dependence
openapi: 3.1.0
info:
  title: FinceptQuantLib API - Risk Module
  description: >-
    Professional-grade risk management endpoints including Value at Risk (VaR),
    stress testing, copulas, extreme value theory (EVT), XVA calculations,
    sensitivities, and portfolio hedging. Part of the Pro Tier (5 credits per
    request).
  version: 3.0.0
  contact:
    name: Fincept API Support
    url: https://fincept.in
    email: support@fincept.in
servers:
  - url: https://api.fincept.in
    description: Fincept API Production Server
security:
  - APIKeyHeader: []
tags:
  - name: quantlib-risk
    description: Risk Management Module - Pro Tier (5 credits/request)
    x-displayName: Risk
paths:
  /quantlib/risk/tail-risk/tail-dependence:
    post:
      tags:
        - quantlib-risk
      summary: Calculate Tail Dependence Coefficient
      description: >-
        Measures the probability that two assets experience extreme losses
        simultaneously. Tail dependence is critical for portfolio
        diversification as assets may appear uncorrelated in normal times but
        become highly correlated during market crashes. Essential for risk
        parity strategies and crisis risk management. [Tier: PRO, Credits: 5]
      operationId: tail_dependence
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - returns1
                - returns2
              properties:
                returns1:
                  type: array
                  description: Return series for first asset
                  items:
                    type: number
                  example:
                    - 0.01
                    - -0.03
                    - 0.02
                returns2:
                  type: array
                  description: Return series for second asset
                  items:
                    type: number
                  example:
                    - 0.015
                    - -0.025
                    - 0.018
                threshold_quantile:
                  type: number
                  description: Quantile threshold for defining tail events
                  example: 0.95
                  default: 0.95
            example:
              returns1:
                - 0.008
                - -0.025
                - 0.012
                - -0.042
                - 0.018
              returns2:
                - 0.01
                - -0.028
                - 0.015
                - -0.038
                - 0.02
              threshold_quantile: 0.9
      responses:
        '200':
          description: Tail dependence coefficient
          content:
            application/json:
              schema:
                type: object
                properties:
                  success:
                    type: boolean
                    example: true
                  data:
                    type: object
                    properties:
                      tail_dependence_coefficient:
                        type: number
                        description: >-
                          Lower tail dependence (0 = independent, 1 = perfect
                          dependence in crashes)
                        example: 0.68
              example:
                success: true
                data:
                  tail_dependence_coefficient: 0.68
        '401':
          $ref: '#/components/responses/UnauthorizedError'
        '402':
          $ref: '#/components/responses/InsufficientCreditsError'
        '422':
          $ref: '#/components/responses/ValidationError'
components:
  responses:
    UnauthorizedError:
      description: Authentication information is missing or invalid
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: string
                example: Invalid API key
    InsufficientCreditsError:
      description: Insufficient API credits for this request
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: string
                example: Insufficient credits. This endpoint requires 5 credits.
    ValidationError:
      description: Request validation error
      content:
        application/json:
          schema:
            type: object
            properties:
              detail:
                type: array
                items:
                  type: object
                  properties:
                    loc:
                      type: array
                      items:
                        type: string
                    msg:
                      type: string
                    type:
                      type: string
  securitySchemes:
    APIKeyHeader:
      type: apiKey
      in: header
      name: X-API-Key
      description: >-
        API key for authentication. Get your key at
        https://api.fincept.in/auth/register

````